Apogee One - best input from mixer?

Hi all -

I know this might be overkill but I wanted to get the best quality possible.

Here's what I'm using the One for:

I have regular presentations that I do at hotels for about 350-400 people. I also have several remote attendees. For the remote attendees I will provide access via WebEx which basically shares your screen/presentation over the internet. It also allows you to use voice of IP (VoIP) to transmit audio. Here's what I am thinking of doing:

There will be professional house audio and several microphones for all the presenters. All the microphones obviously feed into a single mixer. There is also sound from the computer being used for the presentations feeding into the mixer. So essentially all audio is fed into the house mixer.

To transmit the audio over the computer to the remote attendees, I am going to use the Apogee One. My question is what input is best to use? The Instrument or Microphone input? And I apologize for this probably basic question, but is there a standard "out" cable for mixers? Do I need to worry about getting conversion cables?